Temporal variation in TiO2 engineered particle concentrations in the Broad River during dry and wet weathers.

Abstract

Titanium dioxide (TiO2) engineered particles are widely used in the urban environment as pigments in paints, and as active ingredients in photocatalytic coatings. Consequently, studies are necessary to quantify TiO2 engineered particle concentrations and their temporal variability in surface waters to gain better understanding about their abundance and environmental fate in order to minimize their potential environmental impacts. The objective of this study was to determine the temporal variability in the concentration of TiO2 engineered particles in the Broad River, Columbia, South Carolina, United States during dry and wet weather conditions and to examine the relationship between flow discharge, water quality indicators, and the concentration of TiO2 engineered particles. TiO2 engineered particle concentration in the Broad River water was determined by mass balance calculation using bulk titanium concentration and the increase in Ti/Nb ratio above the natural background ratio. The relative abundance of single metal and multi-metal Ti-bearing particles was determined by single particle-inductively coupled plasma-time of flight-mass spectrometer (SP-ICP-TOF-MS). Additionally, the elemental ratios of Ti/Nb, Ti/Al, and Ti/Fe within multi-metal Ti-bearing particles were determined at the single particle level. Discharge, bulk elemental concentrations (e.g., Ti, Al, Fe, and Nb), bulk elemental ratios (e.g., Ti/Al, Ti/Fe, and Ti/Nb), TiO2 engineered particle concentration, and turbidity displayed the same trend of rise and fall following storm events. Linear relationships were established between turbidity and TiO2 engineered particle concentrations in the Broad River for different flow regimes. However, no correlation was observed between TiO2 engineered particle concentrations and flow discharge, dissolved oxygen, pH, or ionic strength. The established correlations between turbidity and TiO2 engineered particle concentrations are important as they can be used to translate the continuously monitored turbidity to TiO2 concentrations.